CA2559308C

CA2559308C - Method and system for determining a three dimensional representation of an organ

Info

Publication number: CA2559308C
Application number: CA2559308A
Authority: CA
Inventors: Gera Strommer; Uzi Eichler; Itzik Shmarak; David Peles
Original assignee: MediGuide Ltd
Current assignee: St Jude Medical International Holding SARL
Priority date: 2005-09-23
Filing date: 2006-09-08
Publication date: 2014-12-02
Anticipated expiration: 2026-09-08
Also published as: CA2559308A1; EP1768068A2; IL177923A0; JP5281740B2; US20060064006A1; IL177923A; EP1768068A3; JP2007083048A; EP1768068B1; US7840252B2

Abstract

A method for determining a three dimensional representation of a tubular organ, the method comprising the procedures of registering a three dimensional medical positioning system (MPS) coordinate system with a two dimensional coordinate system, acquiring a plurality of MPS points within the tubular organ, the MPS points are associated with the MPS coordinated system, each of the MPS point is acquired with a respective organ timing signal reading, acquiring at least one two dimensional image of the tubular organ, the at least one two dimensional image is associated with the two dimensional coordinate system, the at least one two dimensional image is acquired from at least one perspective, each of the at least one two dimensional image is further acquired with a respective organ timing signal reading, associated each of the MPS points with the at least one two dimensional image according to the organ timing signals thereof, determining a temporal three dimensional representation of a portion of the tubular organ for each MPS point, the portion being identifiable in the respective two dimensional image.

Description

Method and System for Determining a Three Dimensional Representation of an Organ FIELD OF THE DISCLOSED TECHNIQUE
The disclosed technique relates to organ assessment, in general, and to methods and systems for determining a 3D representation of a tubular organ, in particular.
BACKGROUND OF THE DISCLOSED TECHNIQUE
3D visual representation of an organ assists a physician in assessing the condition of that organ. More particularly, a 3D
representation of a tubular organ, such as a coronary vessel, helps identify and assess plaque burden and lesion dimensions such as length, diameter and volume. Further more, a 3D representation of a tubular organ aids the physician to identify, on a 2D image, regions of foreshortening of the vessel caused by the projection of the 3D vessel on a 2D plane. Additionally, with the aid of the 3D representation of the tubular zo organ, a physician can identify bifurcation points of that tubular organ.
U.S. patent 6,169,917, entitled "Method and Device for Reconstructing Three-Dimensional Images of Blood Vessels, Particularly coronary vessel, or Other Three-Dimensional Structure" to Masotti et al, directs to a method wherein three X-Ray images, from three different perspective are provided. A reference object, comprising two planes, integral with the patient, containing at least six points with known three-dimensional coordinates, opaque to the image radiation, provides the perspective transformations associated with each angiographic image.
Using these transformations, and a set of points of projection of a three-dimensional object, the three-dimensional object is reconstructed.
The reconstruction is determined using a semi-automatic algorithm. Initially, a starting point and an initial direction of the vessel are determined. From thereon, the next segment of the vessel, whose length is proportional to the actual radius thereof, is identified. The segment is identified according to the probability that the vessel proceeds in a given direction. This probability is determined by calculating the mean gray level contained in a rectangular mask which is rotated about the point belonging to the center line of the vessel.
U.S. patent 6,148,095 entitled "Apparatus and Method for Determining Three-Dimensional Representation of Tortuous Vessel" to Prause et al, directs to an apparatus and method for reconstruction of the coronary vessel, generated from ECG-gated intravascular ultrasound (IVUS) frames obtained by a catheter, combined with biplane angiography.
Initially, the IVUS catheter is positioned at the distal end-point of the designated vessel. The IVUS catheter is withdrawn at a fixed speed while biplane X-ray images are acquired. The IVUS catheter obtains ultrasound

-2-images from within the vessel during the withdrawal. Since either the catheter, or the lumen borders or both are present on the biplane X-ray images, a 3D representation of the centerline of the vessel can be reconstructed. Using this 3D centerline representation in conjunction with information about the physical properties of the catheter a 3D pullback path of the catheter is determined. The IVUS images are then mapped to the determined 3D pullback path according to the pullback speed and catheter twist. The gaps between adjacent IVUS slice are filled by interpolation. The IVUS images are further correlated with the activity lo phase of the heart. The activity phase of the heart is obtained by Electrocardiogram (ECG), to ensure that the images are obtained under consistent conditions.
U.S. patent 6,047,080 entitled "Method and Apparatus for Three-Dimensional Reconstruction of Coronary Vessel from Angiographic Image" to Chen et al, directs to a method for reconstruction of a 3D
coronary arterial tree from routine biplane angiograms acquired at arbitrary angles and without using calibration objects. According to the method directed to by Chen et al, a plurality of 2D images of a target object is acquired. On each image, the centerlines of the vessels are identified.
Using these centerlines, a vessel hierarchy data structure, including the identified 2D vessel centerlines is created. By traversing the corresponding vessel hierarchy data structure, a predetermined number of bifurcation points are calculated. Using the calculated bifurcations points,

-3-corresponding to each of the projected image, the rotation matrix and translation vector representing the relative orientation of the images are determined. Using these rotation matrix and translation vector, the correspondence between the 2D centerlines, corresponding to each image, is established and a 3D vessel centerline is calculated. A 3D visual representation, of the target object, is reconstructed based on the 3D
vessel centerline and diameter of each vessel, estimated along the 3D
centerline of each vessel. Consequently, the optimal views, of the vessel segments, with minimal vessel foreshortening, are determined.
U.S. Patent 6,456,271 entitled "Vascular Reconstruction" to Reidfeld, directs to a method and apparatus for reconstructing blood vessels in three dimensions. A catheter, including a position sensor, is advanced into the blood vessel and the position of the sensor is acquired at a plurality of points in the vessel. Based on these points, a centerline and the inner surface of the blood vessel are calculated. The plurality of points is fitted to a parametric representation of the vessel centerline.
Each coordinate dimension, in the parametric representation, is represented by a polynomial. The inner surface of the blood vessel is reconstructed about the centerline by generating a tube of either fixed or variable radius. This tube is generated by determining plurality of unit vectors, sampling the circle around the centerline, and multiplying these unit vectors by the radius of the tube. The radius is determined by averaging the distances of the points from the centerline. A

-4-reconstruction, with variable radius, is achieved by averaging the distances of a plurality of points in a vicinity of interest. Alternatively, the radius may be selected by the user. Using the centerline and the radius a wire frame of the blood vessel is generated and the rectangular patches composing the wire frame are shaded.

-5-SUMMARY OF THE PRESENT DISCLOSED TECHNIQUE
It is an object of the disclosed technique to provide a novel method and system for determining a three dimensional representation of a tubular organ.
In accordance with the disclosed technique, there is thus provided a method for determining a three dimensional representation of a tubular organ comprising the procedures of registering a three dimensional medical positioning system (MPS) coordinate system with a two dimensional coordinate system. Acquiring a plurality of MPS points within the tubular organ, the MPS points are associated with the MPS
coordinated system, each of the MPS point is acquired with a respective organ timing signal reading. Acquiring at least one two dimensional image of the tubular organ, the at least one two dimensional image is associated with the two dimensional coordinate system, the at least one two dimensional image is acquired from at least one perspective angle, each of the at least one two dimensional image is further acquired with a respective organ timing signal reading. Associating each of the MPS
points with the at least one two dimensional image according to the organ timing signals thereof. Determining a temporal three dimensional representation of a portion of the tubular organ for each MPS point.
In accordance with another aspect of the disclosed technique, there is thus provided a system for determining a three dimensional representation of a tubular organ. The system comprising an organ timing

-6-signal detector, a medical imaging system, a medical positioning system (MPS), a catheter fitted with an MPS sensor, and a processor. The medical imaging system is associated with a two dimensional coordinate system. The MPS is associated with a three dimensional MPS coordinate system. The processor is coupled with the MPS, with the organ timing signal detector and with the medical imaging system. The MPS is coupled with the organ timing signal detector and with the MPS sensor fitted on the catheter. The processor is coupled with the MPS, the organ timing signal detector and with the medical imaging system. The organ timing signal detector acquires an organ timing signal reading representing the activity state of the organ. Medical imaging system acquires at least one two dimensional image from at least one perspective. The at least one least one two dimensional image is associated with a respective organ timing signal reading. The catheter is inserted into the tubular organ and the MPS acquires a plurality of MPS points. Each of the MPS points is associated with a respective organ timing signal reading. The processor registers the three dimensional MPS coordinate system with the two dimensional coordinate system, associates an organ timing signal reading with each of the MPS points and with each of the at least one two dimensional image and determines a three dimensional representation of the tubular organ.

-7-BRIEF DESCRIPTION OF THE DRAWINGS
The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:
Figure 1, is a schematic illustration of a system for determining a 3D representation of a tubular organ;
Figures 2A, 2B, 2C, 2D, 2E and 2F are schematic illustrations of exemplary two 2D images of tubular organ 150 acquired from two different perspective angles and the resulting cross section and 3D representation of tubular organ 150;
Figure 3A and 3B are a schematic illustration of three 2D
images, of tubular organ in the body of a patient, acquired at three different activity states of the organ, and the MPS points acquired during these three different activity states;
Figure 4 is a schematic illustration of a method for determining a 3D representation of a tubular organ;
Figure 5 is a method for determining a 3D model of a tubular organ;
Figure 6 is a schematic illustration of and image 380 of a tubular organ;
Figure 7 is a schematic illustration of a tubular organ 300 infected by lesions 302 and 304; and

-8-Figure 8 is a schematic illustration of a 2D image generally reference 330 of tubular organ 332.

-9-DETAILED DESCRIPTION OF THE EMBODIMENTS
The disclosed technique overcomes the disadvantages of the prior art, by providing a method and a system for determining a 3D
representation of a tubular organ. A plurality of Medical Positioning System (MPS) points, representing the positions of an MPS sensor, within the tubular organ, are acquired. The MPS sensor is fitted on a catheter and is associated with a 3D MPS coordinate system. This catheter may be a Guided Measurement Catheter (GMC), a diagnostic catheter (e.g., Ultra Sound imaging catheter) or a therapeutic catheter (e.g., stenting io catheter or an ablating catheter). Additionally, a contrast dye is injected into the tubular organ and at least one 2D image (e.g., X-ray image, magnetic resonance image, positron emission tomography image or ultrasound image), from at least one perspective angle, of that tubular organ, is acquired. The 2D
image is associated with a 2D coordinate system. The contrast dye highlights the tubular organ in the image. The 2D coordinate system is registered with the 3D MPS coordinate system ( e.g., by an optical¨magnetic calibration procedure). After the MPS points are acquired, a 3D representation of the tubular organ is determined and displayed.
The MPS points represent the 3D trajectory of the MPS sensor within the tubular organ. This 3D trajectory is projected on the 2D image, thereby defining the centerline of the tubular organ on that 2D image. The 2D borders of the tubular organ, identifiable on the 2D image, are detected

-10-.

according to the defined centerline, by an image segmentation process. A
3D circle is generated around each MPS point, the diameter of the 3D
circle being the distance between the detected borders at the respective MPS point. This 3D circle defines the 3D border of the 3D representation of the tubular organ.
When only a single 2D image is used, the resulting 3D
representation of the tubular organ is limited to a circular cross section.
However, the tubular organ might have an oval cross section or other arbitrary cross sections. Therefore, a plurality of 2D images, from different lo perspective angles of the tubular organ, are acquired. The contour of the 3D border is refined according to the detected 2D border points of the tubular organ on each 2D image, and the resulting cross section is a closed curve.
During acquisition of the MPS points and the 2D image, or images, the inspected tubular organ may move. This motion affects the MPS sensor readings (e.g., position and orientation). Therefore, while acquiring MPS point readings and 2D images, the system simultaneously acquires organ timing signals of organs (e.g., the heart, the lungs). These organ timing signals represent the activity state of the organs.
Accordingly, each of the MPS points and each 2D image are associated with a respective organ timing signal reading. Consequently, each MPS
point is associated with a respective 2D image according to the organ timing signals thereof. Thus, a unique 3D trajectory, of the MPS sensor, is

-11-defined for each activity state and therefore for each 2D image. This unique 3D trajectory is projected on the respective 2D image when the centerline of the tubular organ is defined as described above.
Reference is now made to Figure 1, which is a schematic illustration of a system for determining a 3D representation of a tubular organ, generally referenced 100, constructed and operative in accordance with another embodiment of the disclosed technique. In the following description of system 100, the inspected tubular organ is assumed stationary (i.e., the tubular organ is not moving). System 100 includes medical imaging system 118 associated with a 2D coordinate system, a Medical Positioning System (MPS) 124 associated with a 3D MPS
coordinate system, an organ timing signal detector 126, a processor 128, a catheter 106, a display unit 122 and a table 104. Medical imaging system 118 includes an imaging radiation transmitter 120 and an imaging radiation detector 116. Medical positioning system 124 includes MPS
transmitters 110, 112 and 114, reference sensor 130 and an MPS sensor (not shown).
Processor 128 is coupled with organ timing signal detector 126, with imaging radiation detector 116, with MPS 124 and with Display unit 122. MPS 124 is coupled with organ timing signal detector 126 and with catheter 106. The MPS sensors (not shown) are coupled with distal end 108 of catheter 106. MPS transmitters 110, 112 and 114 are coupled with imaging radiation detector 116.

-12-Catheter 106 is inserted into tubular organ 134 and MPS 124 acquires a plurality of MPS points within tubular organ 134. Medical imaging system 118 acquires at least one 2D image of tubular organ 134 from at least one perspective. The 2D images are provided to processor 128. Processor 128 registers the 3D MPS coordinate system with the 2D
coordinate system and projects the 3D trajectory of the catheter on each of the 2D images. Thus, the centerline of the tubular organ on the respective 2D image is defined. Using this centerline and image processing techniques, processor 128 detects the 2D borders of a portion of organ 134 identifiable on the respective 2D image. Using these 2D borders and the MPS points, processor 128 determines a 3D representation of a portion of the tubular organ. Display 122 displays 3D representation 132 of organ 134. Display 122 may further display 3D representation 132 of organ 134 superimposed on a 2D image.
Reference is now made to Figures 2A, 2B, 2C, 2D, 2E and 2F
which are schematic illustrations of exemplary two 20 images of tubular organ 150 acquired from two different perspective angles and the resulting cross section and 3D representation of tubular organ 150 in accordance with another embodiment of the disclosed technique. In the following description of Figures 2A, 2B, 2C, 2D, 2E and 2F, the inspected tubular organ is assumed stationary. Both 2D images (Figures 2A and 2C) include centerline 152 which is defined by projection of the 3D trajectory of a catheter. The 3D trajectory is determined by MPS points 154, 156 and

-13-158. Using centerline 152, border points 160 and 162 (Figure 2A) and border points 166 and 168 (Figure 2C) of tubular organ 150 are detected.
These detected border points are used to define the constraints of the closed curve that will define the 3D borders of tubular organ 150. In this exemplary case, these constraints are the distance between border points 160 and 162 (Figure 2A), and the distance between border points 166 and 168 (Figure 2C). These distances define diameters of circles. Using these defined diameters, a circle is generated around each MPS point. In Figure 2B, the diameter of circle 164 corresponds to the distance between io border points 160 and 162 (Figure 2A) at MPS point 156 (Figure 2A) as detected from the first perspective. In Figure 2D, the diameter of circle 170 corresponds to the distance between the border points 166 and 168 (Figure 2C) at MPS point 156 (Figure 2C) as detected from the second perspective. Thus, a contour 172 (Figure 2E) is traced from circle 160 and 162. Contour 172 has the shape of an ellipse since it is generated from two circles. After repeating for each MPS point, a 3D model, such as 3D
model 132 (Figure 2F and Figure 1) is determined.
The inspected organ may move during the acquisition of the MPS points and the 2D image or images. More particularly, when the tubular organ is a coronary artery, the tubular organ is involved in a cyclic motion according to the cardiac cycle, caused by the pressurized flow of blood therein. Therefore, the MPS points are associated with the 2D

-14-images (e.g., by synchronization), according to the organ timing signals acquired simultaneously therewith.
Reference is now made to Figure 3A and 36, which are a schematic illustration of three 2D images, of tubular organ in the body of a patient, acquired at three different activity states of the organ, and the MPS points acquired during these three different activity states, in accordance with a further embodiment of the disclosed technique. The first image of the organ, designated 1801, was acquired at a first activity state Tl. The second image of the organ, designated 1802, was acquired io at a second activity state T2. The third image of the organ, designated 1803, was acquired at a third activity state T3. During activity state -11, MPS points 182, 188 and 194 were acquired. During activity state 1-23 MPS points 184, 190 and 198 were acquired. During activity state T21 MPS points 186, 192 and 196 were acquired. Thus, referring to Figure 3B, centerline 200 is the projection of the catheter 3D trajectory on image 1801. Centerline 202 is the projection of the catheter 3D trajectory on image 1802. Centerline 204 is the projection of the catheter 3D trajectory on image 1803. Using these Centerlines, and image segmentation, the borders, such as borders 206 and 208 are detected. A circle is generated around each MPS point, using the distance between these borders, at a particular MPS point, as the diameter of the respective circle.
Referring back to Figure 1, Catheter 106 is inserted into tubular organ 134 and MPS 124 acquires a plurality of MPS points within organ

-15-134. Medical imaging system 118 acquires at least one 2D image of tubular organ 134 from at least one perspective. Simultaneously, organ timing signal detector 126 detects the activity state of the organ. Thus, each MPS point and each 2D image is associated with an organ timing signal reading. Organ timing signal detector 126 detects the organ timing signal from the acquired MPS points, by filtering periodic motions of the MPS sensor (not shown) relative to reference sensor 130. Detecting organ timing signals from MPS points is further described in U.S. patent application 10/986567.
Alternatively, organ timing signal detector 126 is an Electrocardiogram (ECG) detector fitted with body surface electrodes. In accordance with another embodiment of the disclosed technique, each of medical imaging system 118 and MPS 124 has a different organ timing signal detector.
Processor 128 registers the 3D MPS coordinate system with the 2D
coordinate system. Processor 128 associates each MPS point with the corresponding 2D image according to the detected organ timing signals.
Reference is now made to Figure 4, which is a schematic illustration of a method for determining a 3D representation of a tubular organ in accordance with a further embodiment of the disclosed technique.
In procedure 220, a 3D MPS coordinate is registered with a 20 coordinate system. Consequently every point in the 3D MPS coordinate system is mapped to a point in the 20 coordinate system. With reference to Figure

-16-1, processor 128 registers the 3D MPS coordinate system with the 2D
coordinate system.
In procedure 222, a plurality of MPS points, within a tubular organ, with a respective organ time signal reading for each MPS point, are acquired. The MPS points are acquired with a catheter, fitted with an MPS sensor, into the tubular organ. The MPS points are acquired during the insertion of the catheter or during a manual or automatic pullback of the catheter. The organ timing signal associated with each MPS point reading represents the activity state of the organ during the acquisition of the MPS point. With reference to Figure 1, MPS 124 acquires a plurality of MPS points, within organ 134, with an MPS sensor coupled with distal end 108 of catheter 106. The organ timing signals are detected by organ timing signal detector 126.
In procedure 224, at least one 2D image of a tubular organ is acquired form at least one angle perspective angles of the organ, with a respective organ timing signal reading for each image. Prior to the acquisition of the at least one 2D image, a dye is injected into the tubular organ. This dye may be injected by the catheter acquiring the MPS points.
With reference to Figure 1, medical imaging system 118 acquires at least one 2D image of tubular organ 134 from at least one perspective. The organ timing signals are detected by organ timing signal detector 126.
After procedures 220 and 222 the method proceeds to procedure 224.

-17-In procedure 226, each of the MPS points is associated with the 2D images, according to the organ timing signals thereof. Thus, each MPS point is associated with a respective 2D image. With reference to Figure 1, processor 128 associates each of the MPS points with a respective 2D image detected by imaging radiation detector 116.
In procedure 228, a temporal 3D representation of a portion of the tubular organ, is determined for each MPS point, with the MPS point and from the borders of the tubular organ, identifiable in the respective 2D
image. Determining the 3D representation is further explained in lo conjunction with Figure 5. With reference to Figure 1, Processor 128 determines a 3D representation of a portion of the tubular organ, for each MPS point, from the MPS point and from the 2D border of the tubular organ, identifiable in the respective 2D image. 3D representation 132 is displayed on display 132.
In procedure 230, the determined 3D representation is superimposed on a 2D image. The 3D representation may be projected on any of the at least one 2D images. The 3D representation may further be projected on a real time 2D image. Therefore, the system selects a desired angle of perspective of the real time 2D and projects the 3D
representation on that real time 2D image. Furthermore, when the 3D
representation is projected on a real time 2D image, the 2D projection of the 3D representation can function as a virtual dye. Therefore, there is no need to inject a dye into the tubular organ prior to the acquisition of the

-18-real time 2D image. Furthermore, the disclosed technique further enables to identify bifurcation points of the tubular organ. Virtual dye and bifurcation points are further illustrated in conjunction with Figure 6. It is noted that bifurcation points can be identified on the 3D representation.
With reference to Figure 1, processor 128 projects the determined 20 representation on one of the 2D images and displays it on display 122.
Reference is now made to Figure 5, which is a method for determining a 3D model of a tubular organ in accordance with another embodiment of the disclosed technique. In procedure 250, at least one 2D
io image is selected, the image includes the tubular organ.
With reference to Figure 1, processor 128 selects one or more 2D images.
In procedure 252, the 3D trajectory of the catheter, determined by the associated MPS points, is projected on each selected 2D image.
Thereby, a centerline of the tubular organ is defined. With reference to Figure 1, processor 128 projects the 3D trajectory of the catheter on the selected 2D image, thereby, defining the centerline of the tubular organ.
In procedure 254, the 2D border points of the tubular organ, on the selected image, are detected. These 2D border points are detected using the defined centerline and image processing techniques. These image processing techniques may be for example edge detection. With reference to Figure 1, processor 128 detects the borders of the tubular organ on the selected image.

-19-=

In procedure 256, a 3D closed curve is generated around each MPS point, associated with each selected image. The detected 2D border points, at each MPS point, determines the constraints of that closed curve (e.g., the circumference of the closed curve must included these border points). In the case wherein 2D images, of the tubular organ, were acquired from only one perspective, the closed curve is a circle. The diameter of that circle is the distance between the detected 2D borders of the tubular organ. When, for example, the 2D images of the tubular organ were acquired from two different perspectives, the refined contour will io have the shape of an ellipse. In the case wherein more then two 2D
images were acquired, the shape of the closed curve is arbitrary. With reference to Figure 1, processor 128 generates a 3D closed curve around each MPS point associated with the selected image.
Reference is now made to Figure 6, which is a schematic illustration of image 280 of a tubular organ in accordance with a further embodiment of the disclosed technique. 2D projection 282of a 3D
representation of the tubular organ is superimposed on image 280. 2D
projection 282 serves as a virtual dye of the tubular organ. Thus, there is no need to inject a dye into the tubular organ prior to the acquisition of the image 280.
Furthermore, point 284 is identified as a bifurcation point.
According to the disclosed technique, a bifurcation point is determined when after identifying only two borders for one MPS point, now for the next

-20-MPS point, the system identifies at least three borders, with a gap between two adjacent ones. The bifurcation point resides in the transition area between these two MPS points. The system then verifies that this is indeed a bifurcation point with the aid of another 2D image, from another perspective angle of the tubular organ.
In some cases, the inspected tubular organ may be infected with lesions or plaque. Consequently, the determined borders may be those of the lesion within the tubular organ and not the actual borders of the tubular organ.
Reference is now made to Figure 7, which is a schematic illustration of a tubular organ 300 infected by lesions 302 and 304 in accordance with another embodiment of the disclosed technique.
According to MPS points 306, 308 and 310, borders 312 and 314 were determined as the borders of tubular organ 300. However, borders 312 and 314 do not represent the true borders of tubular organ 300. When the 3D representation of the tubular organ is displayed, as described in conjunction with Figure 4, the physician may notice that borders 312 and 314 are not the true borders of tubular organ 300. Therefore, the physician selects MPS points 306 and 310 as reference points for the true width of tubular organ 300. True borders 316 and 318 are determined (e.g., by interpolation) according to the width between borders 312 and 314 at MPS points 306 and 310. Furthermore, using true borders and the lesion borders, characteristics, such as the position, the length and the

-21-volume of the lesion can be determined. When, for example, a procedure of placing a stent device in an artery is performed, a mark, representing the location of the lesion may be superimposed on a real time image of the artery. Consequently, the physician can accurately navigate the stenting catheter to the location of the lesion.
When a 3D representation of an object is projected on a 2D
image, the true dimensions of the object may be distorted. For example, a sphere will appear as a circle if projected onto a 2D image plane. When the object is a tubular organ within the human body, such as a coronary artery, that tubular organ may curve "into" or "out of" the image plane.
Thus, the true length of the tubular organ may be distorted. This phenomenon is called foreshortening. Since the 3D representation of the tubular organ was constructed from a 3D trajectory of a catheter, within the tubular organ, the system provides the physician with information is regarding the true length of the displayed tubular organ. Furthermore, the system provides the physician with a representation of the true length of the tubular organ on the 2D image.
Reference is now made to Figure 8, which is a schematic illustration of a 20 image generally reference 330 of tubular organ 332 in accordance with a further embodiment of the disclosed technique. In Figure 7, 3D trajectory 334 of tubular organ 332 is projected on 20 image 330. A plurality of equally spaced markers points 336 are marked on 3D
trajectory 334. The space between each pair of marker points 336 on 3D

-22-trajectory 334 is a tangible unit of length (e.g., 1 millimeter). 3D
trajectory 334 and marker points 336 are projected on 2D image 330.
Consequently, where the foreshortening phenomenon worsens, the distance between adjacent pairs of marker points 336, on the plane of 2D
image 330, is observed to decrease. Thus, the physician has both a quantitative assessment of the true length of tubular organ 330 and a visual aid to asses the foreshortening phenomenon on 2D image 330.
According to a further aspect of the disclosed technique, the system colors the marker points 336 differently for different levels of foreshortening. The io level of foreshortening is determined, for example, according to the ratio between the lengths of the projection of the organ, on the 2D image, to the true length of the organ (i.e., the length of the 3D trajectory). Where this ratio is small, the foreshortening phenomenon is prominent and the markers are colored, for example, red. Where this ratio is large, the foreshortening phenomenon is not prominent and the markers are colored, for example, green.
The foreshortening phenomenon may worsen or lessen according the angle of perspective of the organ. According to another embodiment of the disclosed technique, with reference to Figure 1, processor 128 automatically selects the perspective angle of medical imaging system 118 where the foreshortening phenomenon is the least prominent and recommends that perspective angle to the physician.

-23-It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.

-24-

Claims

CLAIMS:

1. A method for determining a three dimensional representation of an organ, said method comprising the procedures of:
registering a three dimensional medical positioning system (MPS) coordinate system with a two dimensional coordinate system;
acquiring a plurality of MPS points within said organ, said MPS points are associated with said MPS coordinated system, each of said MPS points is acquired with a respective organ timing signal reading;
acquiring at least one two dimensional image of said organ, said at least one two dimensional image is associated with said two dimensional coordinate system, said at least one two dimensional image is acquired from at least one perspective angle, each of said at least one two dimensional image is further acquired with a respective organ timing signal reading;
associating each of said MPS points with said at least one two dimensional image according to the organ timing signals thereof;
determining a temporal three dimensional representation of a portion of said organ for each MPS point, said procedure of determining a three dimensional representation comprising the sub-procedures of:
selecting at least one two dimensional image, said at least one two dimensional image including said organ;
projecting a trajectory of a catheter on the selected two dimensional image, said trajectory being determined by said MPS points associated with said selected two dimensional image, thereby defining a centerline of said organ;
detecting the border points of the organ on said selected two dimensional image;
and generating a three dimensional closed curve around each of said MPS points associated with said selected image.

2. The method according to claim 1, wherein said acquiring at least one two dimensional image occurs while dye is present in said organ.

3. The method according to claim 1 further includes the procedure of superimposing said three dimensional representation on a two dimensional image.

4. The method according to claim 3, wherein said two dimensional image is a real time two dimensional image, said real time two dimensional image being associated with an organ timing signal readings.

5. The method according to claim 3, wherein said two dimensional image is one of said at least one two dimensional image.

6. The method according to claim 3, wherein the perspective of said two dimensional image is selected such that a foreshortening phenomenon is minimized, said foreshortening phenomenon caused due to the super position of said three dimensional representation on the plane of said two dimensional image.

7. The method according to claim 3, wherein a two dimensional projection of said superimposed three dimensional representation serves as a virtual dye instead of injecting a dye prior to acquiring said real time two dimensional image.

8. The method according to claim 1, wherein said plurality of MPS points are acquired by inserting a catheter, fitted with an MPS sensor into said organ.

9. The method according to claim 1, wherein said organ timing signal is an electrocardiogram signal.

10. The method according to claim 9, wherein said electrocardiogram signal is filtered from said plurality of MPS points.

11. The method according to claim 1, wherein said at least one two dimensional image is a type selected from the group consisting of:
X-ray image;
Magnetic resonance image;

Positron emission tomography image; and Ultrasound image.

12. The method according to claim 1, wherein said procedure of determining a three dimensional representation of said portion of said organ is determined from said MPS points and the borders of said organ, said borders being identifiable on said at least one two dimensional image.

13. The method according to claim 1, wherein said border points are detected according to said defined centerline and image processing techniques.

14. The method according to claim 1, wherein a plurality of equally spaced marker points are determined on said three dimensional trajectory for providing a visual true length assessment of said organ when said trajectory is projected on said two dimensional image, thereby providing a visual assessment of foreshortening.

15. The method according to claim 14, wherein said markers are colored according to the level of said foreshortening.

16. The method according to claim 14, wherein the space between said markers is one millimeter.

17. A system for determining a three dimensional representation of an organ, said system comprising:
an organ timing signal detector for acquiring an organ timing signal reading, said organ timing signal reading represent the activity state of an organ;
a medical imaging system for acquiring at least one two dimensional image from at least one perspective, said medical imaging system being associated with a two dimensional coordinated system, said at least one two dimensional image being associated with a respective organ timing signal reading;
a medical positioning system (MPS), coupled with said organ timing signal detector, said MPS being associated with a three dimensional MPS coordinate system, for acquiring a plurality of MPS points, each of said MPS points being associated with a respective organ timing signal reading;
a catheter, fitted with an MPS sensor, for insertion into said organ said MPS
sensor is coupled said MPS;
a processor, coupled with said MPS, with said organ timing signal detector and with said medical imaging system, for registering said three dimensional MPS
coordinate system with said two dimensional coordinate system, for associating an organ timing signal reading with each of said MPS points and with each of said at least one two dimensional image and for determining a three dimensional representation of said organ by:
selecting at least one two dimensional image, said at least one two dimensional image includes said organ;
projecting a trajectory of a catheter on the selected two dimensional image, said trajectory being determined by said MPS points associated with said selected two dimensional image, thereby defining a centerline of said organ;
detecting the borders of the organ on said selected two dimensional image; and generating a three dimensional closed curve around each of said MPS points associated with said selected image.

18. The system according to claim 17, wherein said acquisition of said at least one two dimensional image occurs while dye is present in said organ.

19. The system according to claim 17, further including a display for displaying said three dimensional representation.

20. The system according to claim 17, wherein said processor is further operative for superimposing said three dimensional representation on a real time two dimensional image, said real time two dimensional image being associated with an organ timing signal readings.

21. The system according to claim 19, wherein said display is further operative to display said three dimensional image is superimposed on a two dimensional image.

22. The system according to claim 21, wherein said two dimensional image is a real time two dimensional image.

23. The system according to claim 19, wherein a two dimensional projection of said superimposed three dimensional representation serves as a virtual dye instead of injecting a dye prior to acquiring said real time two dimensional image.

24. The system according to claim 21, wherein said processor is further operative to select the perspective of said two dimensional image, such that a foreshortening phenomenon is minimized, said foreshortening phenomenon is caused due to the projection of said three dimensional representation on the plane of said two dimensional image.

25. The system according to claim 17, wherein said organ timing signal is an electrocardiogram signal.

26. The system according to claim 25, wherein said processor is further operative to filter said electrocardiogram signal from said plurality of MPS points.

27. The system according to claim 17, wherein said at least one two dimensional image is a type selected from the group consisting of:
X-ray image;
Magnetic resonance image;
Positron emission tomography image; and Ultrasound image.

28. The system according to claim 17, wherein said processor is further operative for determining said three dimensional representation from said MPS points and the borders of said organ, said borders being identifiable on said at least one two dimensional image.

29. The system according to claim 17, wherein said processor is further operative for detecting said border points according to said defined centerline and image processing techniques.

30. The system according to claim 17, wherein said processor is further operative for determining a plurality of equally spaced marker points on said three dimensional trajectory for providing a visual true length assessment of said organ when said trajectory is projected on said two dimensional image.

31. The system according to claim 30, wherein said markers are colored according to a level of foreshortening.

32. The system according to claim 30, wherein the space between said markers is one millimeter.

33. A system for determining a three dimensional representation of an organ, said system comprising the following:
a processor, configured to be coupled with (a) an organ timing signal detector configured to acquire an organ timing signal reading representing an activity state of an organ, (b) a medical imaging system configured to acquire at least one two-dimensional image from at least one perspective, said medical imaging system being associated with a two-dimensional coordinate system, said at least one two-dimensional image being associated with a respective organ timing signal reading, (c) a medical positioning system (MPS), coupled with said organ timing signal detector and associated with a three-dimensional MPS coordinate system, for acquiring said plurality of MPS points, each of said MPS points being associated with a respective organ timing signal reading, and (d) a catheter, fitted with an MPS sensor coupled to said MPS, configured to be used in association with said organ, said processor being adapted to (i) register the three-dimensional MPS coordinate system with the two-dimensional coordinate system, (ii) associate an organ timing signal reading with each of said plurality of MPS
points and with each of said at least one two-dimensional images, and (iii) determine a three-dimensional representation of said organ by:
selecting at least one two-dimensional image including said organ;
projecting a trajectory of said catheter on the selected two-dimensional image, said trajectory being determined by said MPS points associated with said selected two-dimensional image, thereby defining a centerline of said organ;
detecting borders of said organ on said selected two-dimensional image;
and generating a three-dimensional closed curve around each of said MPS
points associated with said selected two-dimensional image.

34. The system according to claim 33, wherein said acquisition of said at least one two dimensional image occurs while dye is present in said organ.

35. The system according to claim 33, further including a display for displaying said three dimensional representation.

36. The system according to claim 33, wherein said processor is further operative for superimposing said three dimensional representation on a real time two dimensional image, said real time two dimensional image being associated with an organ timing signal readings.

37. The system according to claim 35, wherein said display is further operative to display said three dimensional image is superimposed on a two dimensional image.

38. The system according to claim 37, wherein said two dimensional image is a real time two dimensional image.

39. The system according to claim 35, wherein a two dimensional projection of said superimposed three dimensional representation serves as a virtual dye instead of injecting a dye prior to acquiring said real time two dimensional image.

40. The system according to claim 37, wherein said processor is further operative to select the perspective of said two dimensional image, such that a foreshortening phenomenon is minimized, said foreshortening phenomenon is caused due to the projection of said three dimensional representation on the plane of said two dimensional image.

41. The system according to claim 33, wherein said organ timing signal is an electrocardiogram signal.

42. The system according to claim 41, wherein said processor is further operative to filter said electrocardiogram signal from said plurality of MPS points.

43. The system according to claim 33, wherein said at least one two dimensional image is a type selected from the group consisting of:
X-ray image;
Magnetic resonance image;
Positron emission tomography image; and Ultrasound image.

44. The system according to claim 33, wherein said processor is further operative for determining said three dimensional representation from said MPS points and the borders of said organ, said borders being identifiable on said at least one two dimensional image.

45. The system according to claim 33, wherein said processor is further operative for detecting said border points according to said defined centerline and image processing techniques.

46. The system according to claim 33, wherein said processor is further operative for determining a plurality of equally spaced marker points on said three dimensional trajectory for providing a visual true length assessment of said organ when said trajectory is projected on said two dimensional image.

47. The system according to claim 46, wherein said markers are colored according to a level of foreshortening.

48. The system according to claim 46, wherein the space between said markers is one millimeter.